This invention is directed to non-sticky gels of ethylenically unsaturated monomer solutions containing isocyanurate resins and which are particularly useful as sheet molding compounds. Of particular interest are polyvinylisocyanurate resin polyol blends which can be molded into intricately shaped articles having a high loading of glass fibers and which can be copolymerized with the ethylenically unsaturated monomer at relatively moderate temperatures. In particular it is directed to gelled vinylidene monomer solutions of ethylenically unsaturated polyisocyanurate resins by employing mixed polyurethane/polyisocyanurate resins free of ethylenic unsaturation as the gelling or thickening agent. It is also directed to a process for forming gelled solutions wherein a relatively large molar excess of aromatic polyisocyanate is added to a monomer solution of polyisocyanurate resin containing certain primary and secondary polyol reactants. Furthermore, it is directed to thickened ethylenically unsaturated copolymer resin solutions which can be molded and cured at moderate temperatures and pressures to form completely cured polyvinyl isocyanurate resins of low profile or deep drawn reinforced components having a filler content as high as 80%. The fully cured gelled composition retains substantially all the physical properties that would be obtained from a cast vinylisocyanurate/vinyl monomer copolymer containing no polyurethane thickener. Such fully cured vinyl isocyanurate thermoset resin exhibit especially superior tensile and flexural strength at high temperatures.
Molding compositions employing ethylenically unsaturated polyester resins having unreacted carboxyl groups and vinylidene monomers have been thickened by the addition of inorganic materials such as calcium or magnesium oxides. Gellation takes place rather slowly with the employment of these oxides and in some instances require as many as two or three days to obtain a handleable or non-sticky condition. If not molded within a short period of time thereafter, they must be discarded since the gellation and cross-linking continues to a point where the composition is no longer tractable.
More recently, however, cross-linked polyurethane thickened gels of polyester resins have been developed which are an improvement over the metal oxide thickened materials in that they have increased stability and can be maturated to form moldable compositions within a few hours. Such systems after complete curing exhibit improved shrinkage characteristics over the cured metal oxide cross-linked and thickened materials. Both linear and cross-linked polyurethane copolymers have been used for ethylenically unsaturated polyester resins and are described in U.S. Pat. Nos. 3,047,530; 3,290,208; 3,464,935; 3,644,569; 3,700,752; 3,859,381; 3,868,431; 3,886,229; 3,893;956; 3,962,370; 3,994,764; 3,997,490; 4,062,826; and 4,073,828. In many ways, the systems described for the thickening of ethylenically unsaturated polyester resins/monomer solutions are similar to that of the invention. However, when isocyanurate resins are substituted for polyester resins in the ethylenically unsaturated polymer-in-monomer solutions, incompatability and incomplete maturation problems lead to the formation of cottage cheese or sticky jelly-like gels which can neither be shaped, handled or used to form uniformly filled molded objects.
In recent years the automobile industry has been striving to reduce weight of most newly manufactured vehicles as a means for increasing gas mileage. A most attractive way to reduce weight is to switch from metal to light-weight plastic components. However, plastics are inherently weak and must be highly reinforced to meet tensile strength requirements of certain components such as wheels, brackets and structural panels. In order to meet this strength requirement, resins must be reinforced with materials such as glass fiber filaments in high concentrations, mostly exceeding 50% by weight. Compositions having large amounts of filler, while producing very strong completely cured resins are difficult to mold into articles having uniformly distributed reinforcing materials. In producing molded articles having intricate shapes wherein a preform containing fibrous filler is squeezed between the male/female sections of the mold and the flowout exceeds 30%, it is difficult to obtain a uniformly filled article. Usually resin material flows away from the fibrous filler leaving the article more highly filled in the region of the preform and scantily filled at the mold extremities or locations of maximum flowout.
In extruding and molding conventional ethylenically unsaturated polyester resins, a high concentration of fiberglass reinforcing agent is required to produce a molded article having suitable strength. However, as the concentration of fiberglass is increased, the amount of thickening agent such as a conventional cross-linked polyurethane must also be increased. When the concentration of urethane is increased, the amount of available polyester resin is decreased, thereby diluting the high strength and flexibility characteristics of the fully cured base resin. With the combination set forth in the present invention, physical properties, such as flex strength and heat distortion temperature, are not adversely affected by the use of larger amounts of thickening agent as demonstrated by the examples. It is now possible to make thickened polyisocyanurate glass reinforced articles of complex shape having better uniformity and strength throughout.
It has now been found that ethylenically unsaturated polyisocyanurates, such as poly(1,3,5-tri-R substituted S triazine-2,4,6trione) may be thickened and copolymerized with unsaturated monomer R groups containing ethylenic unsaturated materials. R groups may also be linked with epoxy, polyurethane and polyester resins. Such isocyanurates are well-known as represented by U.S. Pat. Nos. 2,952,665; 3,041,313; 2,821,098; 3,850,770; 3,719,638; 3,437,500; 3,947,736 and 3,762,269. Of particular interest are polyvinyl isocyanurates described in copending U.S. Application Ser. Nos. 819,352 and 819,353 to Markiewitz et al. and which are also assigned to ICI Americas Inc. For the purposes of this invention, polyisocyanurate resins can be considered as cross-linked networks of isocyanurate rings having ethylenically substituted aromatic pendant groups. Aromatic rings may be linked to ethylenically unsaturated moieties through carbamyl, urylene, ether, carbonyl, carboxyl and combinations thereof. In most instances satisfactory resins are prepared by reacting a polyisocyanate with a hydroxyl-terminated ethylenically unsaturated compound such as ethylenically unsaturated monohydroxy alcohols, monohydroxy ethylenically unsaturated esters, monoamino ethylenically unsaturated esters, monohydroxy ethylenically unsaturated ureas, ethylenically unsaturated monoamines, ethylenically unsaturated hydroxylamines and polyalkoxylated vinyl alcohols to name a few. Monohydroxy compounds are reacted under conditions which favor the reactivity with only one isocyanate per molecule of the polyisocyanate aromatic compound. It is well understood, however, that a substantial quantity of polyisocyanate molecules go completely unreacted while others go completely reacted to form polyurethanes.
It has now been found that improved blends are useful in preparing non-sticky molding compositions by the reaction therewith of polyisocyanates comprising:
5-95% by weight of a polyethylenically unsaturated polyisocyanurate resin,
5-95% by weight of an ethylenically unsaturated monomer, and
1.5-30% by weight of relatively non-polar polyol free of ethylenic unsaturation having a molecular weight in the range of 300-2,000 selected from the group consisting of polyether glycols of ethylene glycol, polyhexamethylene glycol, aromatic ethers which are condensation products of propylene oxide, and dihydroxy terminated polyesters derived from glycols, polyether glycols and dicarboxylic acids.
These blends are converted to tack-free molding compositions by the addition of polyisocyanate such that the mol ratio of the hydroxyl groups in the blend to the isocyanate groups in the added polyisocyanate ranges from 0.66-0.95.
Of particular interest are isocyanurates of urethanes of an aromatic polyisocyanate and at least one vinylidene carbonyl oxy alkanol characterized by one of the following formulae: ##STR1## wherein R.sub.1 is hydrogen or an alkyl group containing from 1 to 4 carbon atoms, R.sub.2 is hydrogen, alkyl containing from 1 to 12 carbon atoms, or a chlorinated, brominated, or fluorinated alkyl group containing from 1 to 12 carbon atoms, R.sub.3 is hydrogen, alkyl containing from 1 to 12 carbon atoms, or a chlorinated, brominated, or fluorinated alkyl group containing from 1 to 12 carbon atoms, R.sub.4 is hydrogen, methyl or ethyl, and n is from one to four, with the proviso that R.sub.2 and R.sub.3 on adjacent carbon atoms are not both alkyl or chlorinated, brominated, or fluorinated alkyl, that is at least one of R.sub.2 and R.sub.3 must be hydrogen. In order to obtain resins having the excellent combination of high temperature physical properties provided by the present invention, it is essential that the resin be prepared from an unsaturated isocyanurate composition wherein at least a major amount of the isocyanurate moieties are based on one or more vinylidene carbonyl oxy alkanols defined above. Illustrative examples of such alkanols include; hydroxypropyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, and diacrylates and dimethacrylates of trimethylol propane, trimethylol ethane, trimethylol methane, and glycerol. A preferred group of vinylidene carbonyl oxy alkanols include hydroxypropyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, and blends thereof. Another preferred group of such alkanols are blends of polyfunctional acrylates or methacrylates such as pentaerythritol triacrylate, pentaerythritol trimethacrylate, and mixtures thereof, with one or more monofunctional acrylates or methacrylates such as hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate.
While the isocyanurates of this invention must contain moieties derived from one of the vinylidene carbonyl oxy alkanols defined above, the moieties derived from an aromatic polyisocyanate may be based on any trimerizable aromatic polyisocyanate. In fact, any trimerizable aromatic polyisocyanate which is conventionally used in the art for the preparation of isocyanurates may be used to prepare the isocyanurate compositions of the present invention. For example, the aromatic polyisocyanate may or may not contain ethylenic unsaturation and it may be monomeric or polymeric. The only requirements are that the aromatic polyisocyanate contain at least two aromatic isocyanate groups, be trimerizable, and be free of any groups which interfere with the trimerization of isocyanate groups or which interfere in the reaction of an isocyanate group with a hydroxyl group. Illustrative examples of aromatic polyisocyanates which are particularly useful in the preparation of isocyanurate compositions of this invention include: 2,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; m-phenylene diisocyanate; p-phenylene diisocyanate; 1,5-naphthalene diisocyanate; 4,4'-diphenyl ether diisocyanate; 4,4',4"-triphenylmethane triisocyanate; 2,4,4'-triisocyanatodiphenylmethane; 2,2',4-triisocyanato diphenyl; 4,4-diphenylmethane diisocyanate; 4,4'-benzophenone diisocyanate; 2,2-bis(4-isocyanatophenyl)propane; 1,4-naphthalene diisocyanate; 4-methoxy-1,3-phenylene diisocyanate; 4-chloro-1,3-phenylenediisocyanate; 4-bromo-1,3-phenylene diisocyanate; 4-ethoxy-1,3-phenylene diisocyanate; 2,4'-diisocyanatodiphenyl ether; 4,4'-diisocyanatodiphenyl; 9,10-anthracene diisocyanate; 4,6-dimethyl-1,3-phenylene diisocyanate; 4,4'-diisocyanatodibenzyl; 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane; 3,3'-dimethyl-4,4'-diisocyanatodiphenyl; 3,3'-dimethoxy-4,4'-diisocyanatodiphenyl; 1,8-naphthalene diisocyanate; 2,4,6-tolylene triisocyanate; 2,4,4'-triisocyanatodiphenyl ether, diphenylmethane diisocyanate, polymethylene polyphenylene polyisocyanate available under the trademarks Rubinate M and Papi, having a functionality of 2.1 to 2.7; 1,3-xylene 4,6-diisocyanate; aromatic isocyanate terminated polyurethanes; and aromatic isocyanate terminated pre-polymers of polyesters. Although it is preferred to use all aromatic polyisocyanate, small amounts of an aliphatic polyisocyanate, for example, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, or alpha,alpha'-diisocyanato-p-xylene, may be used in combination with the aromatic polyisocyanate.
The unsaturated isocyanurate resins can be envisioned as chains and three dimensional networks of isocyanurate rings having urethane linked aromatic vinylidene side chains. Because of the nature of the reactants involved and the catalyst used, not all the isocyanate groups undergo reaction to form isocyanurate and urethane linkages but in fact, a substantial quantity of allophanate and uretidine dione structures maybe formed. In most instances, the polyisocyanurate resins are substantially free of unreacted isocyanate groups. The polyisocyanurate resin normally contains less than about 400 isocyanurate rings or their equivalent per molecule and vary in molecular weight from 2,000 to 200,000. Prior to curing, the solid isocyanurates are fusable and exhibit a softening point as determined by the ring and ball method described in ASTM designation E 28-58T.
Isocyanurate resins may be prepared by reacting an aromatic polyisocyanate with one or more of the described vinylidene hydroxy compounds to form an isocyanate-containing urethane to form the ethylenically unsaturated isocyanurate resin. The --NCO/OH mol ratio in the reaction mix is maintained at a range at from 0.75 to 1.6 and preferably from about 0.9 to about 1.4. When the reaction is carried out in equal parts of an inert-solvent and the reactants are hydroxypropyl methacrylate and toluene diisocyanate, the preferred mol ratio for sheet molding applications range from 0.95 to about 1.05.
In carrying out the trimerization reaction, the temperature must be maintained such that the vinylidene group does not undergo the additional polymerization prematurely. Usually the reaction is carried out in a range of 0.degree. to about 95.degree. C.
Up to about 49 mol percent of the vinylidene carbonyl oxy alkanol described in the list above may be replaced with a monohydric alcohol selected from methanol, ethanol, propanol, butanol, isobutanol, octyl alcohol, cyclohexanol, benzyl alcohol, allyl alcohol, glycerol diallyl ether, trimethylolpropane diallyl ether, saturated halogenated alcohols, halogenated alcohols containing ethylenic unsaturation, for example, dibromoneopentyl glycol monoacrylate and monomethacrylate, halogenated allyl alcohols, monohydric alcohols such as 2-bromo ethanol, 3-bromo-1-propanol, 4-chloro-1-butanol, 2-chlorethanol, 4-chloro-1-hexanol, 3-chloro-1-propanol, 2,3-dibromo-1-propanol, 2,3-di-chloro-1-propanol, 2,2,2-trichloroethanol, 1-bromo-2-propanol, 1-chloro-2-propanol, 1,3-dibromo-2-propanol, and 1,3-dichloro-2-propanol, mono acrylate and mono methacrylate esters of alkoxylated bisphenol A and alkoxylated tetra bromobisphenol A, and polyoxyethylene and polyoxypropylene ether of monohydric phenols.
Illustrative examples of dihydric alcohols which may be used to replace up to 33 mol percent, and preferably up to 10 mol percent, of the vinylidene carbonyl oxy alkanols described include: ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, compounds characterized by the formula: ##STR2## wherein R.sub.1 is an alkyl group containing from 1 to 4 carbon atoms, 1,4-butane diol, pentamethylene glycol, hexamethylene glycol, glycerol methyl ether, polyoxyethylene and polyoxypropylene ethers of dihydric phenols such as bisphenol A, glycerol monochlorohydrin, glyceryl monostearate, dihydroxy acetone, and monoesters of the above polyols and acrylic acid or methacrylic acid.
The unsaturated isocyanurate compositions of this invention may be homopolymerized or copolymerized with one or more other ethylenically unsaturated copolymerizable compounds. Where the unsaturated isocyanurate composition of this invention is to be copolymerized with monomer, the isocyanurate composition may be dissolved in the copolymerizable monomer or it may be desirable to utilize the copolymerizable compound as a solvent for the reaction system in which the ethylenically unsaturated isocyanurate compositions of this invention are formed. If the ethylenically unsaturated copolymerizable monomer is to be used as a solvent for the preparation of the unsaturated isocyanurate products, the solvent should not contain any groups which would react with isocyanate groups or in any way interfere with the urethane formation reactions or trimerization reactions which occur in the formation of the isocyanurate products of this invention. Thus, the solvent should not contain any hydroxyl, carboxyl, or amine groups which might interfere with these reactions. This limits the suitable solvents to esters, ethers, hydrocarbons and similar solvents containing non-reactive groups. Illustrative examples of solvents which may be employed in the preparation of the isocyanurate products of this invention include: divinyl benzene, styrene, meythl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, butyl acrylate, butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, chlorostyrene, acrylonitrile, vinylidene chloride, vinyl acetate, vinyl stearate, vinyltolylene, hexandiol diacrylate, hexanediol dimethacrylate, tetrahydrofurfuryl methacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, allyl methacrylate, diallyl fumarate, tetramethylene glycol diacrylate, trimethylolpropane triacrylate, neopentyl glycol diacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, polyethylene glycol diacrylate, dimethylstyrene, ethylstyrene, propylstyrene, para-chloromethyl styrene, meta-dibromoethyl styrene, bromo styrene, dichloro styrene, t-butyl styrene, vinyl propionate, and vinyl butyrate. Nonpolymerizable solvents may also be used, for example, benzene, toluene, xylene, and ethylbenzene. The solvent may be removed from the reaction mixture after the formation of the isocyanurate to give a solid product. The solid product may be dissolved in the same or a different polymerizable solvent prior to curing. Mixtures of solvents may also be used. Preferred solvents are styrene, a mixture of styrene and methyl methacrylate, and a mixture of styrene and divinylbenzene.
When the isocyanurates are prepared in the absence of solvent, the product formed is a solid and requires special processing which permits the easy removal of the heat generated by the reaction and which prevents the reaction mixture from reaching high temperatures which may induce insolubility and gelation of the products. Among these special processing techniques may be the trimerization of the monourethane in thin layers on moving temperature-controlled belts or in temperature controlled trays.
The amount of solvent employed to dissolve the isocyanurate compositions of this invention may vary over a very wide range. The particular amount of solvent used will depend somewhat on the nature of the solvent and on the solubility of the particular isocyanurate used. The polymeric character of the isocyanurate product allows maintenance of adequate working viscosity at relatively low concentrations of dissolved solids. Products of this invention may be made which permit adequate laminate working viscosity, which is defined as 100 to 10,000 centipoises Brookfield as determined on a Brookfield Viscometer, Model LVT, #2 spindle, at 30 rpm., at 25.degree. C. The amount of solvent will also depend on the nature of the properties desired in the final cured product. Thus, if one is interested in preparing a copolymer of styrene and an isocyanurate of a monourethane of tolylene diisocyanate and hydroxypropyl methacrylate, for example, the high temperature properties of the final product will increase as the concentration of the styrene decreases. In general, however, the amount of solvent used will be from 5 to 95 weight percent of the total composition and preferably from 30% to 80% by weight of the total composition. A particularly preferred concentration is about 50% by weight.
Suitable catalyst for carrying out the urethane formation of step 1 of the above process in addition to copper salt, are: organo-metallic compounds of tin, zinc, lead, mercury, cadmium, bismuth, cobalt, manganese, antimony, iron and the like such as, for example, metal salts of carboxylic acids having from about 2 to about 20 carbon atoms including for example stannous octoate, dibutyl tin dilaurate, dibutyl tin diacetate, ferric acetyl acetonate, lead octoate, lead oleate, cobalt naphthanate, lead naphthanate, mixtures thereof and the like. It is preferred that the catalysts be employed in liquid form. Those catalysts which are not ordinarily liquids may be added as a solution in solvent. It is best to carry out the urethane reaction in the absence of a trimerization catalyst in order to reduce premature thickening.
The trimerization of isocyanates is usually carried out in the presence of such catalysts as tertiary amines, organic quarternary ammonium hydroxide compounds, diones, metallic salts of carboxylic acids, alkoxides or phenoxides of alkali or alkaline earth metals, organic phosphines, organo-metallic compounds of tin, animony and the like. The catalyst concentration in the reaction may range from 0.01-3.0% based on the total weight of the resin.